新疆中天山地块花岗岩隆升剥露过程及对区域找矿潜力的制约

Uplift-Exhumation Process of Granitoids from the Central Tianshan Terrane and Its Constraints to the Ore-Prospecting Potential,Xinjiang Province

新疆中天山地块位于中亚造山带东南部,区内矿产资源丰富,是我国西北部重要的多金属矿产分布区,成矿作用与岩浆活动密切相关。在野外地质调查基础上,对区内7个花岗岩体进行磷灰石裂变径迹分析。结果表明,磷灰石裂变径迹年龄变化范围为124~54 Ma,径迹长度介于(12.3±2.3)~(13.2±1.8)μm,显示该区磷灰石径迹形成后以较慢速度通过部分退火带,后期未发生明显升温。结合前人数据发现,花岗岩裂变径迹年龄可分为124~114 Ma、94~92 Ma、79~54 Ma 3组,分别对应3期区域性构造事件。温度-时间热史模拟结果表明,样品大多经历两个阶段的快速隆升期,分别为160~120 Ma和70~30 Ma。通过定量计算得出中天山地块内花岗岩体中—新生代剥蚀量为1.4~2.4 km,剥蚀速率0.011~0.036 mm/a。剥蚀深度与区内彩霞山铅锌矿、沙东和小白石头钨矿等中低温矿床成矿深度相似,对矿床保存不利。区内阿拉塔格铁矿、天宇-白石泉铜镍矿及尾亚铁矿等高温矿床成矿深度远大于花岗岩体剥蚀深度,推测中天山地块深部仍具较好的矽卡岩型铁矿床、铜镍硫化物矿床及钒钛磁铁矿床找矿潜力。

The Central Tianshan Terrane is located at southeast of the Central Asian Orogenic Belt(CAOB).It is rich in mineral resources and is an important polymetallic mineral distribution area in Northwest China.Mineralization is closely related to magmatism.Based on the detailed field geological survey.Apatite fission track analysis was carried out on 7 granite bodies in the area.The results show that the apatite fission track pooled age ranges from 124~54Ma,with the mean track lengths varying from 12.3±2.3 to 13.2±1.8μm,indicating that these samples have passed through the partial annealing zone at a slower speed,and there is no obvious reheating event in the later stage.Combined with the previous achievements,the fission track ages of apatite from the granites in the Central Tianshan Terrane can be divided into three groups,124~114 Ma,94~92 Ma and 79~54 Ma,in accordance with three times of regional tectonic activities in western China.The further temperature-time modeling of fission track indicates that there are two exhumation events during the Mesozoic-Cenozoic time(160~120Ma and 70~30Ma,respectively).According to the quantitative calculation,the Mesozoic-Cenozoic denudation depth of granites in the Central Tianshan Terrane ranges from 1.4 to 2.4km,and the denudation rate changes from 0.011 to 0.036 mm/a.This denudation depth is similar to the mineralization depth of the Caixiashan Pb-Zn deposit,Shadong W deposit,Xiaobaishitou W-(Mo)deposit and other meso-hypabyssal deposits,suggesting that the denudation degree is unfavorable for the preservation of this type deposit.However,the mineralization depth of Alatage Fe deposit,Tianyu,Baishiquan Cu-Ni sulfide deposit and Weiya Fe deposit in the area is far greater than the denudation depth of granites.Therefore,it is suggested that the depth area of the Central Tianshan Terrane should be a favorable place for ore-prospecting of skarn iron deposits,Cu-Ni sulfide deposit and V-Ti magnetite deposits.